The invention is based on a brake system with anti-skid control for motor vehicles.
In a known brake system with anti-skid control (German Offenlegungsschrift 36 12 793), both brake circuits are so-called static brake circuits, into which a brake pressure determined by the brake pedal stroke is fed, each from one brake chamber of the master brake cylinder. Such brake systems have a high hydraulic power requirement.
In a brake system of the type initially referred to above, contrarily, upon actuation of the brake pedal brake pressure is fed directly from the pressure reservoir into the dynamic brake circuit, which preferably includes the wheel brake cylinders of the two rear wheels. At the same time, the first brake chamber of the master brake cylinder is acted upon by this brake pressure, which causes the master brake piston to be displaced and a corresponding brake pressure for the static brake circuit of the front wheels to be built up in the second brake chamber of the master brake cylinder. If the pressure should fail, then by means of brake pedal actuation, the master brake piston is displaced via the emergency brake piston, so that brake pressure is generated only in the static brake circuit. Brake systems of this kind are structurally simpler.
In a known brake system of this type, the master brake piston and the emergency brake piston are disposed in separate work cylinders and mechanically connected to one another via a tappet extending through the partition between two work cylinders. The brake pedal is coupled to the emergency brake piston via a brake rod, which after a displacement travel sufficient for brake valve control, in the event of a disruption in pressure generation, form-fittingly carries the emergency brake piston along with it in the displacement direction. The partition defines the first brake chamber of the master brake cylinder on one side, and on the other a counterpressure or return chamber of the emergency brake piston, into which chamber, upon anti-skid control, a variably high pressure is fed for pressure modulation; this pressure urges the emergency brake piston in the restoring direction, as a result of which the master brake piston effects a brake pressure modulation in the brake circuits. The pressure modulations in the restoring chamber are transmitted in full to the brake pedal and are annoyingly perceptible by the driver.